1. Technical Field
The present invention relates to a crimping structure for attaching an electrical cable to a terminal, and more particularly to a crimping structure of a terminal to an electrical cable, in which the electrical cable having a conductor formed of an aluminum or an aluminum alloy is attached to the terminal, and when the electrical cable is pulled so that a force of detaching the electrical cable from the terminal is exerted thereon, the aluminum electrical cable can be prevented from being easily disconnected.
2. Background Art
In general, copper electrical cables are used for wire harnesses to be wired in vehicles, such as an automobile. When the wire harnesses are connected with each other or in-vehicle devices, a terminal is attached to the copper electrical cables of the wire harnesses. This type of terminal is generally attached to the copper electrical cables by crimping.
The terminal crimped on the copper electrical cable generally includes a bottom plate adapted to allow a conductor of the copper electrical cable, which is formed by twisting a plurality of copper wires together, to be placed thereon, and a pair of conductor caulking pieces provided to be continuous to the bottom plate and thus to allow the conductor placed on the bottom plate to be sandwiched therebetween.
The pair of conductor caulking pieces is adapted such that, by inwardly crimping the conductor caulking pieces, the conductor of the copper electrical cable is sandwiched between the bottom plate and the conductor caulking pieces, and, by sandwiching in this way, the terminal is crimped on the conductor of the copper electrical cable.
In recent years, use of an aluminum electrical cable instead of the copper electrical cable has been studied in consideration of weight reduction of vehicles and easy recycling of material, in addition to the lack of copper resources. However, the aluminum has a thick oxide film formed on a surface thereof, as compared to the copper, and in a case of the aluminum electrical cable, a contact resistance between the conductor and the terminal tends to be relatively high.
To reduce the contact resistance between the conductor and the terminal, a method is employed, in which each of the conductor caulking pieces of the terminal is strongly caulked on the conductor so that a compression ratio of the conductor is increased. According to this method, the oxide film on each of wires constituting the conductor is broken by strongly caulking the conductor, thereby achieving a reduction of the contact resistance between the conductor and the terminal.
As used herein, the compression ratio of the conductor is a ratio of a cross-sectional area of the conductor after compression to a cross-sectional area of the conductor before compression.
As the compression ratio of the conductor is increased, a stress applied to the conductor is also increased. Accordingly, in the case of the aluminum which is inferior in mechanical strength to the copper, a crimping strength of the terminal is significantly reduced if an excessive stress is applied to the conductor.
Therefore, with respect to crimping the terminal to the aluminum electrical cable, a crimping structure of a terminal to an electrical cable has been proposed, in which the reduction of the contact resistance between the conductor and the terminal can be compatible with ensuring of the crimping strength of the terminal (for example, see JP-A-2009-181777).
According to the crimping structure disclosed in JP-A-2009-181777, a terminal 10 includes a bottom plate 20 adapted to allow a conductor 2 of an aluminum electrical cable 1 to be placed thereon, and a pair of conductor caulking pieces 21 provided to be continuous to the bottom plate 20 and also to allow the conductor 2 on the bottom plate 20 to be sandwiched and caulked therebetween. The conductor 2 is disposed on the bottom plate 21 between the pair of conductor caulking pieces 21 and is sandwiched between the pair of conductor caulking pieces 21 and the bottom plate 20 by crimping the pair of conductor caulking pieces 21. Also, a protruded portion 24 is provided to be located toward a distal end of a crimped portion of the crimped conductor 2. A caulking height H from the bottom plate 20 to the conductor caulking pieces 21 is substantially constant throughout the entire width of the conductor caulking pieces. Therefore, the crimped portion is more strongly compressed against the protruded portion 24 by the conductor caulking pieces 21 at a distal end side of the conductor 2 than at a proximal end side thereof.
Also, in the crimping structure disclosed in JP-A-2009-181777, a plurality of serrations (shallow grooves) 25 are provided at a rear of the protruded portion 24 on the bottom plate 20 of the conductor holing part 13 to be extended in parallel to each other in a direction perpendicular to an axis direction (i.e., a longitudinal direction of the terminal 10) of the crimped portion of the conductor 2. Thus, the protruded portion 24 is disposed at front of the location where the serrations 25 are provided.
According to the crimping structure disclosed in JP-A-2009-181777, while the caulking height of the whole of the conductor caulking pieces is managed to be substantially constant, a compression ratio of the conductor at a front location where the protruded portion exists can be set higher and a compression ratio of the conductor at a rear location where the protruded portion does not exists can be set lower. Accordingly, an electrical connection ability can be maintained high in a front part having a high compression ratio and a terminal holding force can be maintained high in a rear part having a low compression ratio.
However, JP-A-2009-181777 has problems in that, when core wires of the conductor formed by twisting a plurality of aluminum or aluminum alloy wires together are excessively compressed, the conductor is damaged by corners of the serrations, thereby decreasing a fixing strength, and as a result, when the aluminum electrical cable is pulled, elongation of the conductor of the aluminum electrical cable is small, thereby causing the conductor to be prematurely disconnected or the like.
Also, a terminated aluminum electrical cable, in which a terminal is attached to an aluminum electrical cable, can be used in various environments, and thus a thermal shock test is performed thereto. The thermal shock test is a test intended to evaluate a product by a sudden change in temperature (thermal shock), in which a high temperature and a low temperature are alternately and repeatedly applied to a test product in a short time to cause a sudden change of environmental temperature, thereby evaluating the reliability of the test product.
In the thermal shock test as described above, due to difference in expansion coefficient in a portion where different materials are caulked, a small gap is created between the conductor of the aluminum electrical cable and the bottom plate and the conductor caulking pieces of the terminal by expansion and contraction according to temperature changes. Therefore, there is a case where the conductor of the aluminum electrical cable plays in the conductor caulking pieces.
Because the conductor of the aluminum electrical cable plays in the conductor caulking pieces as described above, there is a problem in that core wires of the conductor, which is formed by twisting a plurality of aluminum or aluminum alloy wires together and is caulked by the conductor caulking pieces, are subject to damage, such as scars, by corners of the serrations, thereby decreasing the fixing strength.
Accordingly, the present invention has been made keeping in mind the above problems, and an object of the invention is to provide a crimping structure of a terminal to an electrical cable, in which, when the electrical cable is pulled so that a force cable of detaching the electrical cable from the terminal is exerted thereon, a stress due to corners of serrations can be prevented from being directly applied thereto, and thus, due to a strain relief effect or a dispersion effect, the conductor of the aluminum electrical cable can be prevented from being easily disconnected.